This invention relates to the concentration or evaporation of liquids, and more particularly to methods and apparatus for increasing the solids content of liquid-solids mixtures.
When industrial wastes are being processed, it is usually beneficial to increase the solids content of any liquid being disposed of. This is particularly true for pulp and paper mill liquid wastes, which ordinarily have a final solids content of up to about 63%. Attempts to increase the solids content of such wastes have involved increasing the number of heat transfer tubes used in conventional evaporation apparatus and processes in order to increase the energy applied to any given volume of liquid waste. It has been discovered that as more of such tubes are used to process a given volume of liquid waste, a point is reached at which the salts from the waste, such as calcium and/or sodium sulfate, that plate out on the heat transfer tubes become the limiting factor in the efficiency of the process.